1. Field of the Invention
This invention is in the field of cyclic char burning engines and gasifiers wherein the cycle of compression followed by expansion is created by a combined compressor and expander means such as a piston and cylinder type of internal combustion engine mechanism.
2. Description of the Prior Art
Examples of prior art cyclic char burning engines and gasifiers are described in the following U.S. Patents:
U.S. Pat. No. 4,372,256; J. C. Firey, Feb. 8, 1983 PA0 U.S. Pat. No. 4,412,511; J. C. Firey, Nov. 1, 1983 PA0 U.S. Pat. No. 4,653,436; J. C. Firey, Mar. 31, 1987 PA0 U.S. Pat. No. 4,794,729; J. C. Firey, Jan. 3, 1989.
In these example cyclic char burning engines and gasifiers air, or other reactant gas containing appreciable oxygen gas, is compressed into the pore spaces of a solid char fuel, contained within a separate primary reaction chamber, during a compression process and this is followed by expansion of the primary reacted gases, formed by reaction of oxygen with the char fuel, out of the pore spaces of the char fuel during an expansion process. This cycle of compression followed by expansion is repeated. This cycle of compression and expansion is created by a combined means for compressing and expanding, such as a piston operated within a cylinder, wherein the space enclosed by the piston crown and the cylinder walls is a variable volume chamber whose volume varies cyclically when the piston is reciprocated by an internal combustion engine mechanism for driving this combined means for compressing and expanding. Following each expansion process the reacted gases are largely removed from the variable volume chamber by an exhaust means. Fresh air is next supplied into the variable volume chamber by an intake means prior to the next following compression process. Thus an exhaust process followed by an intake process is interposed between each expansion process and the next compression process for a cyclic char burning engine or gasifier as is well known in the art of internal combustion engines. Each compression process occupies a compression time interval which is followed by an expansion process occupying an expansion time interval. The separate primary reaction chamber is contained within a pressure vessel container. A means for preheating the char fuel within the primary reaction chamber is used to bring the char fuel up to that temperature at which it will react rapidly with oxygen in adjacent compressed gases while the engine or gasifier is being started. Thereafter the means for preheating the char fuel can be turned off when the heat of the primary reaction becomes sufficient to keep the char fuel at or above this rapid reaction temperature. During starting a cranking means is used to drive the internal combustion engine mechanism. The detailed descriptions of cyclic char burning engines and gasifiers contained in the above listed U.S. Patents are incorporated herein by reference thereto.
The term char fuel is used herein and in the claims to include highly carbonaceous and largely solid fuels such as coal, coke, charcoal, petroleum coke, etc.
As char fuel is reacted to ashes within the primary reactor it is replaced by a refuel mechanism means for supplying fresh char fuel into a refuel end of the primary reactor. The char fuel is thus moved along through the primary reactor toward an opposite ash collection end of the primary reactor. Hence the char fuel being reacted within the primary reactor has a direction of motion from the refuel end toward the ash collection end. An ash removal mechanism is used as a means for removing ashes from the primary reaction chamber.
Where air is the reactant gas it is readily available from the atmosphere. In some applications oxygen enriched air or essentially pure oxygen may be used as the reactant gas, as for example in some gasifier uses, and here a source of oxygen rich gas is needed.
The term producer gas is used herein and in the claims to mean those reacted gases emerging from the primary reactor during expansion and this is normally a fuel gas containing carbon monoxide and other components.
The term secondary reacted gas is used herein and in the claims to mean those reacted gases within the secondary reactor, and for engines these are normally essentially complete combustion products containing carbon dioxide and other components.
In engine applications of cyclic char burning engines and gasifiers the variable volume chamber is also a secondary reaction chamber comprising an igniter means for burning the primary reacted gases with secondary air during the expansion process. The needed secondary air is retained outside the char fuel primary reactor during compression. In gasifier applications of cyclic char burning engines and gasifiers no secondary air is thusly retained and thus the variable volume chamber is not a secondary reaction chamber. Hence for cyclic char burning gasifiers the final reacted gas during expansion is the producer gas product from the primary reactor. For both a cyclic char burning engine and a cyclic char burning gasifier network output can be done on the piston, since both the primary and secondary reactions are exothermic and are carried out under varying pressures of the cycle. Herein and in the claims the term power reactor is used to mean either a cyclic char burning engine or a cyclic char burning gasifier.
The term fixed open gas flow connection is used herein and in the claims to mean a gas flow passage which remains open whenever the cyclic char burning engine or gasifer is operating.
The term changeable gas flow connection is used herein and in the claims to mean a gas flow passage which can be opened or closed while the cyclic char burning engine or gasifier is operating. A changeable gas flow connection is opened and closed by a means for opening and closing and this is driven from the internal combustion engine mechanism drive means as is well known in the art of internal combustion engines.
As the char fuel, within the primary reactor, moves along the char fuel motion direction it is preheated by heat transfer from char fuel portions which are further along and are reacting rapidly with oxygen and thus are at a high temperature. Where the char fuel being used is essentially free of volatile matter, as with coke fuel, this preheat zone serves to bring the new char fuel up to its rapid reaction temperature. The char fuel then enters the rapid reaction zone and carbon reacts therein with oxygen to form producer gas. Beyond the rapid reaction zone in the direction of char fuel motion the char fuel is essentially completely reacted to ashes which pass into an ash collection zone at the end of the char fuel motion path.
When the char fuel being used contains volatile matter, as with bituminous coal, the preheat zone also serves to remove the volatile matter from the coal, in part by distillation and in part by reaction to volatile products. In the absence of oxygen appreciable portions of this distilled volatile matter become tars and other portions become fuel gases of essentially hydrocarbon type. These tars from coal volatile matter are undesirable in a cyclic char burning engine or gasifier as they tend to clog up the mechanical components of the internal combustion engine mechanism and to foul any spark igniters used in the secondary reactor. Tars which are exhausted from the cyclic char burning engine or gasifier are also an undesirable air pollutant material.
In prior art, steady pressure, gas producers tar formation from coal volatile matter has been successfully reduced by passing the primary reactant air first into the preheat and volatile matter distillation zone. The emerging volatile matter apparently reacts with oxygen in the air to form oxygenated hydrocarbon type materials which form much less tar. The resulting volatile matter-in-air mixture then passes into the rapid reaction zone. Within the rapid reaction zone the volatile matter-in-air mixture is apparently burned in appreciable part to fully reacted carbon dioxide and steam. The carbon dioxide and steam, plus any unreacted oxygen, then react with carbon in the rapid reaction zone to form producer gas which emerges from the primary reactor. One disadvantage of this method for reducing tar formation is that the initial burning of the volatile matter in air mixture on entering the rapid reaction zone creates very high temperatures there and ash fusion and clinkering may result. These clinkers clog up the motion of the char fuel along the char fuel motion direction and may encase carbon particles and thus prevent complete carbon gasification. Another disadvantage of this method for reducing tar formation is that the carbon dioxide and steam created by burnup of the volatile matter-in-air mixture, react much more slowly with hot carbon in the rapid reaction zone to form producer gas. In prior art, steady pressure, gas producers this latter disadvantage was overcome by use of deeper rapid reaction zones of larger cross sectional area so that the required producer gas reaction could be completed. But when primary producer gas reactors are to be used on cyclic char burning engines or gasifiers such large volume reactors cannot be used since engine compression ratio would be greatly reduced and power producing efficiency also greatly reduced. It would be very desirable to have available a method for reducing tar formation from high volatile matter char fuels which did not produce clinkers and did not require a large volume primary reactor.
In prior art cyclic char burning engines and gasifiers the ashes are removed from the ash collection zone of the primary reactor at the end of the char fuel motion path by an ash removal mechanism. Most such ash removal mechanisms remove a volume of material at intervals and it is necessary to control either the volume, or the interval, or both, so that only ashes, and no unburned char fuel, are removed. While such control means are feasible they are necessarily complex since it is difficult to sense the ash quantity and ash level existing within the ash collection zone. It would be desirable to have available an ash removal means which did not require such sensing of ash level within the primary reactor.